1. Field of the Invention
The present invention relates to a multi-chip module (MCM) package with a heat spreader. More particularly, the present invention relates to a multi-chip module (MCM) package with a heat spreader efficient in heat dissipation.
2. Description of the Related Art
In the semiconductor industry, the manufacture of an IC product can be divided into two stages, including fabrication of bare IC chips and subsequent packaging processes. The bare IC chips are finished with sequential steps of wafer fabrication, circuit design, pattern transfer and wafer cutting. In the subsequent packaging processes, each bare chip is electrically connected to outer signal sources via bonding pads formed thereon, and then encapsulated with a molding material. The packaging processes are for protecting the bare chips from humidity, heat and noise from the environment, and for providing a medium of electrical connection between the bare chip and an outer circuit, such as a printed circuit board (PCB) or some package substrate.
A bare chip is usually electrically connected to a package substrate via wires. As the integration of chips is continuously increased, the multi-chip module (MCM) package is considered to be a promising technique in the future. An MCM package includes a substrate and several chips bonded thereto, wherein the chips are electrically connected to each other via the circuit on the substrate to constitute a complete circuit structure.
For example, dynamic random access memory (DRAM) chips and a central processing unit (CPU) can be bonded to a substrate to form an MCM package structure. Thus, the packaging density is increased so that less space is required, and signal delay between the chips is reduced. Therefore, MCM packages can satisfy the requirement of high performance, and are widely used in communication electronic products and portable electronic products.
FIG. 1 illustrates a cross-sectional view of a conventional multi-chip module (MCM) package. The MCM package 100 includes a substrate 110, two chips 130 and 150, a molding material 170, conductive lines 180 and 182, and solder balls 184. The substrate 110 has an upper surface 112, a lower surface 122, a die pad 114 and many contact pads 116 and 124 thereon, wherein the die pad 114 and the contact pads 116 are disposed on the upper surface 112 of the substrate 110. The contact pads 116 are disposed around the die pad 114, and the contact pads 124 are disposed on the lower surface 122 of the substrate 110.
The chip 130 has an active surface 132, a back surface 142 opposite to the active surface 132, and contact pads 134 and 136 surrounding the active surface 132 of the chip 130, wherein the contact pads 134 surround the contact pads 136. The chip 130 is adhered to the die pad 114 on the substrate 110 via an adhesive 144 on the surface 142, and is electrically connected to the substrate 110 via wires 180 bonded thereto. One end of a wire 180 is bonded to a contact pad 134 on the chip 130, and the other end is bonded to a contact pad 116 on the substrate 110.
The chip 150 has an active surface 152, a back surface 162 opposite to the active surface 152, and contact pads 154 surrounding the active surface 152. The chip 150 is adhered to the central area of the active surface 132 of the chip 130 via an adhesive 164 on the back surface 162, and is electrically connected to the chip 130 via wires 182 bonded thereto. One end of a wire 182 is bonded to a contact 154 on the chip 150, and the other end is bonded to a contact 136 on the chip 130.
In addition, the chips 130 and 150, the upper surface 112 of the substrate 110 and the wires 180 and 182 are encapsulated with a molding material 170, and solder balls 184 are disposed on the contact pads 124 of the substrate 110.
As mentioned above, the chip 130 and the substrate 110 are electrically connected via wires 180, and the two chips 130 and 150 are electrically connected via wires 182 in a conventional MCM package 100. However, since the wires 180 and 182 are long and have small cross-sectional areas, the transmitted signals will decay rapidly, and will be delayed as well. Moreover, the parasitic LC effect will occur during the operation of a high-frequency circuit to cause signal reflection. Therefore, using wires (180/182) as a medium of signal transmission causes severe noise interference and worse electrical properties.
Moreover, as the chips 130 and 150 are operated under high frequency, the temperatures thereof gradually raise because lots of heat is caused by dielectric loss. As the temperature exceeds the upper limit for normal operation of the chip, the inner circuit of the chip functions abnormally or even fails. The heat dissipation of a conventional MCM package 100 is simply achieved via the thermal conduction effect of the molding material 170 and the substrate 110. Unfortunately, the thermal conduction coefficients of the two are so small that the heat from the chips 130 and 150 cannot be dissipated efficiently, and the chips easily function abnormally or even fail.